Edit: Solved, please see solution below, post #2.

I've tried various methods, including using the PrtScr button, and the SnippingTool, but the screenshot image I get is blank. I wonder if it's because the game is using the nGlide wrapper software?

Edit: I just downloaded a trial version of a program called "DxTory", and tried to take a screenshot using it, but unfortunately it repeatedly crashes W8, without managing to take a screenshot.

Launch 3dSetup.exe in game folder. I liked how game looks with DirectX 6. There should be no problems making screenshots with DirectX.

Edit: pressing Shift + PrtScrn should make a screenshot automatically in game folder. Works for me with DirectX 6.

Excellent thanks, that works great.
SHIFT PrtScn copies the in-game image, and I can then paste it from the clipboard in to any paint program for instance.

in my w8.1 system its just [printscreen] and the image is placed in the game folder so c; GalaxyClienty/games/wizardry8 in my case... don't need to press [shift] but you do have to move them out or rename them if you want to keep the images

Yes thanks a lot! I've been stupid, I'm sorry. I just tried this, simply pressing the PrtScn button (without using the SHIFT key), and the screenshot image files were put (or updated) inside the GoG Wizardry 8 game folder - and that's using the nGlide 3dfx voodoo video display setting too.

Unrelated, but on the subject of nGlide, if I run the nGlide settings program found inside the GoG Wiz 8 folder, I can adjust the resolution of the game to fit my monitor, which is a typical basic widescreen model, but I think it looks alright!